Field of the Invention
The present invention relates to a power supply switching circuit which is suitable for use in a semiconductor device supplied with power from a main power supply and a sub power supply, and which switches the supply of power from the main power supply to the sub power supply when the supply of the power from the main power supply is stopped.
Background Art
FIG. 3 is a circuit diagram illustrating a related art power supply switching circuit.
The related art power supply switching circuit is equipped with a main power supply input terminal 200 supplied with a voltage V0 of a main power supply, a sub power supply input terminal 201 supplied with a voltage V1 of a sub power supply, PN junction elements 202 and 203, and an output terminal 204 which outputs a voltage Vout.
FIG. 4 is a sectional structure diagram of a PN junction element of a related art power supply switching circuit.
The PN junction element is realized by defining an N-type region 208 provided in a P-type region 209 of a substrate as a cathode terminal 206 and defining a P-type region 207 provided in the N-type region 208 as an anode terminal 205. Incidentally, the P-type region 209 of the substrate is supplied with the lowest voltage (VSS) to avoid the flow of an extra forward bias current between the P-type region 209 thereof and the N-type region adjacent to the P-type region 209.
The related art power supply switching circuit is intended to achieve the stable supply of power to a semiconductor device by supplying power from the sub power supply in a backup operating state in which power from the main power supply is stopped.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2003-87994